In recent years, unauthorized copying of documents has become more frequent as a result of the spread of copiers. A technique is provided as a countermeasure that inhibits copying of a specific document. The technique that inhibits copying is as follows.
A copier disclosed in patent literature 1 adds copy inhibition information to a document. When the copier reads the document, the copier inhibits copying of the document.
A copier disclosed in patent literature 2 adds conditional copy permission information and a condition (for example, a password) to a document. When the copier reads the document, the copier requests a user to input the condition added to the document. If the input condition is correct, the copier makes a copy of the document. If the input condition is wrong, the copier does not make a copy of the document.